class_docstr: A Mixin for applications that start InteractiveShell instances.
  
  Provides configurables for loading extensions and executing files
  as part of configuring a Shell environment.
  
  The following methods should be called by the :meth:`initialize` method
  of the subclass:
  
    - :meth:`init_path`
    - :meth:`init_shell` (to be implemented by the subclass)
    - :meth:`init_gui_pylab`
    - :meth:`init_extensions`
    - :meth:`init_code`
code: def _user_ns_changed(self, change):
      if self.shell is not None:
          self.shell.user_ns = change["new"]
          self.shell.init_user_ns()
  
imports: from __future__ import absolute_import
  from __future__ import print_function
  import glob
  from itertools import chain
  import os
  import sys
  from traitlets.config.application import boolean_flag
  from traitlets.config.configurable import Configurable
  from traitlets.config.loader import Config
  from IPython.core.application import SYSTEM_CONFIG_DIRS, ENV_CONFIG_DIRS
  from IPython.core import pylabtools
  from IPython.utils import py3compat
  from IPython.utils.contexts import preserve_keys
  from IPython.utils.path import filefind
  from traitlets import Unicode, Instance, List, Bool, CaselessStrEnum, observe
  from IPython.terminal import pt_inputhooks
label_desc: Use image node_id 1 for calling the InteractiveShellApp obj's underlying member method code with example usage: obj._user_ns_changed(change) without return types